Many installed local area networks (LANs) use Ethernet technology. As a link layer protocol in the TCP/IP stack, Ethernet describes how networked devices should format data for transmission to other network devices on the same segment of a network, and how to prepare output data for sending over the network. Ethernet touches both the physical layer (e.g., Layer 1) and the data link layer (e.g., Layer 2) on the open system interconnection (OSI) network protocol model. Packet and frame are two defined units of transmission in Ethernet protocol. An Ethernet frame includes a payload of data being transmitted and addressing information that can identify the physical media access control (MAC) addresses of both sender and receiver. Other information content of the Ethernet frame includes virtual LAN (VLAN) tagging and quality of service information and error-correction information, which can be useful in detecting transmission problems. Each Ethernet frame can be wrapped in an Ethernet packet that can affix several bytes of information used in establishing the connection and marking where the frame starts.
Automotive Ethernet has gained momentum in recent years. For example, Ethernet over single-pair balanced cabling is specified in the IEEE standards 100BASE-T1 and 1000BASE-T1. One of the valued features of these standards is the ability to pass power over same single pair where data is transmitted. Power over data line (PoDL) can be achieved by injecting and collecting power in the lower frequency band. A coupling circuit can be used to inject power into the data line and separate it from the data. Balancing requirement of the data line for emission and noise immunity and electromagnetic compatibility (EMC) can make the coupling circuit design complicated, especially for unshielded twisted pair (UTP) cables.